The present invention relates generally to an oscillator circuit associated with a transmitter device and, more particularly, to a method for electronically aligning the frequency of an oscillator circuit that may be used to drive an infrared transmitter.
An infrared transmitter is designed to broadcast a modulated signal about a carrier frequency, and thus operates in conjunction with an oscillator circuit. It is well known to use a programmable phase lock loop (PLL) design to synthesize the frequency of the oscillator circuit. In this case, a microprocessor may be used in conjunction with the phase lock loop circuit to control the frequency of the oscillator circuit. Although PLL-controlled oscillators achieve good control over the center frequency, these types of circuits typically cost more than a conventional LCR-based oscillator.
In contrast, conventional LCR-based oscillators provide open loop control over the center frequency. Due to variations in the manufacturing process, the center frequency may vary between oscillators. Without a way to electrically control the center frequency of the oscillator, many well known mechanical alignment techniques are typically incorporated into the manufacturing process. In this way, the desired center frequency of the oscillator is accurately established. Unfortunately, manual alignment further increases the manufacturing costs associated with these types of oscillator circuits. The cost associated with mechanical alignment becomes more critical as the circuits are replicated in order to provide multiple channels within a single application.
Therefore, it is desirable to provide a method for electronically aligning the center frequency of an LCR-based oscillator circuit that may be used to drive an infrared transmitter.
In accordance with the present invention, a method is provided for aligning the center frequency of an infrared transmitter. The method comprises the steps of: (a) providing a voltage-controlled oscillator for driving the infrared transmitter, where the oscillator is adapted to receive a bias voltage from a microprocessor; (b) applying a bias voltage to the oscillator; (c) receiving an output signal from the infrared transmitter into an infrared receiver; (d) determining a frequency associated with the output signal; and (e) adjusting the bias voltage based on the frequency associated with the output signal, thereby aligning the center frequency of the infrared transmitter.
For a more complete understanding of the invention, its objects and advantages, refer to the following specification and to the accompanying drawings.